The real stories from inside the F1 paddock

Wheel size in Formula 1

There is no doubting that larger wheels can look pretty good but on the other hand, the larger the wheels and the tyres the heavier they are and thus the more effect they will have on performance. Tests show that as wheel/tyre combinations get bigger, acceleration and fuel economy suffer often quite dramatically with a 10 percent drop in fuel economy between using 15-inch rims and 19-inch rims. Formula 1 has used 13-inch rims for the last 20 years and this is now out of step with the industry which tend to use 15-inch rims with lower profile tyres. In theory this means that a tyre company has less scope to apply the technology learned in F1 to road car tyres. This is not strictly true but it is clear that if one can market tyres that are the same size as those used in F1 there are likely to be more sales. There was talk a year or so ago of Michelin coming into the sport but the French company said that it wanted to increase wheel rims to 18-inches after the first couple of years.

“The 13-inch tyre is no longer relevant to the everyday road user,” says Pirelli’s Paul Hembery. “While 18-inch tyres would be a big step for Formula 1, there are many other motorsport series that already use this size. So there’s scope to go even bigger than that in Formula 1 in years to come. In order to underline F1’s role as a test bed for future mobility solutions, we believe that it benefits everybody to have as close a link between road car tyres and competition tyres as possible. However, we’d like to emphasise that this move is not something that we are actively pushing for, as our role in Formula 1 is not to instigate changes. Instead, it’s to help teams and drivers make the most out of the equipment, regulations and resources they have at their disposal – whatever they decide that framework is going to be.”

Thus the Pirelli test of 18-inch tyres this week at Silverstone was an interesting experiment. The tyres were run by Charles Pic, with the Lotus.

“It was a very early evaluation test and the different tyres and wheels affect the aerodynamics of the car quite a lot, but you could certainly feel that the tyres felt different to those we’re used to on an F1 car,” he explained.”

The objective of the test was to give Pirelli some initial loading information as well as for everyone to see what the cars looked like in this configuration.

“The new tyres looked stunning fitted to the Lotus,” Hembery said. “These are just a prototype concept, but if the teams decided that they wanted us to proceed in this direction, we have the capability to carry on development in this area and come up with a production-ready version in a comparatively short space of time. We’ve heard a lot of opinions already and we look forward to canvassing other opinions in the coming weeks and months. Even though performance wasn’t by any means priority here, the new tyres still behaved exactly in line with our expectations, so we’re clearly potentially at the beginning of a huge development curve, with the wheel and tyre size rules having remained unaltered for many years.”

The key technical advantage of an 18-inch tyre is a stiffer sidewall that helps maintain the structural rigidity of the tyre and also makes it easier for the tyre to maintain a constant pressure – as there is less actual air inside the tyre.

The reality is that if the wheel size changed, the cars would need to be completely redesigned because of the impact of the tyres in the airflow around the cars. The cars are generally changed from year to year so this is not necessarily a problem but it will mean that the philosophy of design will change as engineers try to find the downforce that will be lost with such a change.

“They are more reactive and nervous and on top of that you lose a lot of aero,” Pic said. “It is not even like you are on the aero you use at Monza, it is even less. The combination means you are five or six seconds off the pace.”

Look at the ride height of the car, its massively higher, because of the lack of suspension in the tyre, so the need for more in the actual damper / spring units. This will probably remove lots of the under car aerodynamic effect

Also look at the tyre shape, again very different to the current tyre.

I am not saying that they won’t recover a lot of this lost aerodynamic performance but they wouldn’t with a test mule!

A potential benefit… Well suspension development would be less slightly less F1 specific if more movement in this is needed by having a much more rigid tyre

Both the above statements are true. It’s the increase in vertical spring rate of the tyre that increases the dynamic ride height of the car so much, and the cars don’t have enough adjustability to compensate for that. But that’s easy to solve.

As someone not at all qualified to comment on it, I thought it sounded a bit odd too. But I assumed the bigger wheel and lower profile tyre would be the same overall diameter as the current tyre, especially for an early test where they’re whacking them on a car designed for those sizes. So I wouldn’t think that’d change anything. Size aside though, I would also think a lower profile tyre would be more consistent, with less deflection compared to the huge sidewalls of the current tyres.

I’m thinking Pic’s feeling of a lack of aero is maybe more to do with the new wheels and tyres being fitted to a car that wasn’t designed for them. The car looks to be riding a fair bit higher than normal, so I’m guessing the effect of the floor is reduced. Plus the suspension set up would no doubt be quite different, and without that all designed for it and finely tuned, the aero would be less consistent.

The new tyre / rim combination weighs about 4 kg more, for each corner. That is quite an increase in unsprung weight, not exactly desirable. The weight of the tyre itself doesn’t change much, whereas the new rims are obviously heavier.

I’m no expert, but I believe closer to the ground means greater down force (ground effect) which means greater drag which equals more fuel use. Also the outer circumference of the tyre didn’t change only the wheel size and inner tyre circumference changed if I’m not mistaken. I’m also guessing the car would sit higher with the combination of larger solid wheel and stiffer tyre sidewalls. But they do look different.

The basically do, yes. I’m not sure it’s softening the ride, per se, but it’s allowing a little less travel in the actual suspension. Cars running rims this size will have to be set up differently though, with a little more travel.

As for Hembury’s comments re: relevance – I don’t care, personally, if they’re relevant or not. And in any case, does this mean they’ll be slimming them down from about 12″ wide on the front and 15″ on the rear to, say, 8″ and 10″? I doubt it – the width is just as irrelevant to the average driver, as wheel width that size are usually on supercars and little else cheaper than a Porsche 911.

The 18’s look pretty good. If it would result in the serious car redesign that’s mentioned then that can only be a good thing. There should be a fundamental tech change every year to give the clever men in white coats at the teams the opportunity find different solutions and shake-up the order.

Don’t read much into Pic’s comment. The suspension isn’t set up yet (need to reduce the wheel rate to compensate for the increased ride rate due to the stiffer tire), and the majority of the aero on the car relies on the front wing directing air to specific locations.

If the wheels and tires are a vastly different shape, it’s not going to work in unison anymore and big drops in performance will be felt. Also, there are huge gaps between the wheel and brake ducting, further compromising aero.

Finally, there is what’s called the “Y-250 vortex”, which is a vortex (or very simply, a mini tornado) that is shed by the inner portion of the upper elements of the front wing and is very beneficial downstream on the car; if the big gap between the duct and the wheel, or even merely the unoptimised pairing of wing design and tire shape, dissipates that hugely important vortex then further huge drops in performance will be felt.

Very true, but on a real design the ducts would fill the inside of the wheels anway. That might make for more powerful management of wheel flows if the duct designs aren`t simplified by rules.

Isn`t the Y250 vortex (or is it the X250 if one works for Mclaren?) just an effect of the FIA mandated 500mm centre section? As I understand it, it’s not somrthing anyone aimed to achieve, but having it imposed on you, the best option is to manage it wisely.

To be fair to Pirelli you can’t blame them they pay a lot of money to be associated with F1 and 18 inch is a good market segment to be targeted for thier road tyre sales. All the other reasons are just dressing.

Exactly – for a start, there are examples of road going direct fuel injection engines going back to the 1920’s and electronic engine management systems were developed in the automotive sector in the late 1970’s.

In fact, motorsport as a whole is pretty poor at developing new technologies – you could probably count on your fingers the number of actual innovations that have come from motorsport as a whole (active suspension, the double clutch gearbox and the disk brake, and the last one of those is disputed).

Newey himself pointed out that motorsport is an end user of technology, since the disparity in resources between a motorsport team and a car manufacturer is colossal – the annual research and development budget of Volkswagen Group alone is nearly ten times that of the whole of the F1 grid combined.

No, the answer is always. Do you think companies like Pirelli operate as charities? Even if ‘relevant’ only means relevant in marketing terms, it’s still important. Pirelli want to sell more tyres. Like Michelin, they see having 18″ or similar wheels as a way of doing that. Same as Esso or She’ll boast of their F1 connections for the fuel (even diesel) you buy at the pumps.

F1 lost the keen amateurs doing it for the love of the sport a very very long time ago.

I think your physics may have gone a bit wonky. Irrespective of the volume of air (or nitrogen) inside the tyre, a temperature rise of Xº will produce an increase in pressure of Y Kpa. What may alter the rate of pressure increase with temperature is the less elastic shorter sidewalls of the 18” tyres. This may in fact mean that the pressure rise with temperature is faster with 18” tyres than with the current 13” tyres.

Today’s thick walled tire has lots of air inside. Part of heating the tires to race temps is about raising internal pressure through that heating. A low profile tire is going to have less air, so there will be new effects in a car with fresh tires. Does this mean less of a difference between a cold tire and a hot one? Well, I’m no tire engineer, either.

“The key technical advantage of an 18-inch tyre is a stiffer sidewall that helps maintain the structural rigidity of the tyre and also makes it easier for the tyre to maintain a constant pressure – as there is less actual air inside the tyre.”

The quantity of air inside the tyre does not affect how the pressure changes, although the sidewall stiffness may.

I was on hold on a call precisely with the same aim, which is why when I glanced and no usual preview I scribbled the repeat .. during which couple of seconds my mind flashed with every stage of the system from here and back again that could have induced a latency, and how the glitch was probably between the JavaScript page function and the server cache whilst the db was catching up. Weird glitch, as in interesting, sort of, neither academically particularly, nor commercially under normal blogging scenarios, but a example of asynchronous communications, not going wrong, but doing what they can do. Figuring out what happens in these milliseconds interests me, and is of commercial interest sufficiently often. Sorry that was all too holding on to the apron strings, there Joe! 😉

Bigger than what? The tire size has been unchanged (700) since I can remember. MTBs have a 29 wheel now, but road bikes are the same. It’s controlled by the UCI. They had bigger wheels on the track bikes in back, but as Dr. Chester Kyle (the designer of the USA track bikes and one of my professors) found out, the gains and losses from extremes in either direction cancelled each other out.

Has anyone got, to hand, the figures for the overall diameter of the two different configurations? With hub size increasing but tyre depth decreasing I’m left unsure as to the overall impact on the wheel diameter.

A move to larger wheel size = fundamental redesign of the cars. Therefore, a chance for clever thinking to steal a lead on design. Whatever regs are brought in, the teams will all have clawed back all the lost downforce and performance within a couple of years such is the rate of development. Anything that encourages innovation and radical thinking should be encouraged. The looks are irrelevant. Let us be honest, it hasnt taken long to get used to the new nose designs, they are hardly mentioned now. And the engines now noisier than those who complain about it, rather than vice versa.

I like very much that Pirelli use their voice. They quietly challenge the status quo, whilst, without tugging any real forelocks, point out they are very very humble and have to produce what’s needed. I think they’re doing more for the sport, as a result.

What is needed to help get torque down on to the track in a controlled manner is a larger effective rolling diameter. There is no point in going to low profile tyres unless the outer diameter is greater.
If the dia is greater then the ride height, geometry, roll centre, …everything changes.

There is a great deal more open space between the rim and the hub which means a complete rethink on brake cooling. Aero, start again from scratch.
The volume of air or nitrogen in the tyres is much less than in the current design, thus will react far more to changes in temperature by creating changes in pressure.
Remember your good old P1V1/T1 = P2V2/T2 (P and T are absolute)

However these sorts of tyres last for 4 hours in WEC at often greater speeds than found in F1.

This is not the unknown, there must be vast amounts of data out there on this type of tyre, from other formulae.

Lost me there old chap! If you mean nitrogen then I need to check but it was allowed to use it for inflating tyres, pushing of valves etc.
Though not for pressurising the FRIC system. (though I suspect it will be if active is allowed after all next year.)

The arguments for fuel efficiency are logical, the weight of the 18s aslo interesting, but the real reason for F1 having 13″ rims is because they’ve been like that for many years, and it is too much of a black art for the teams to want to switch off their own backs. Other forms of racing have bigger rims, IndyCar included, and they seem to do just fine.

Like anything else in F1, we all make a big deal out of it and it would be forgotten after 2 races with the new wheel size…then when we looked back the 13s would look strange.

I can see that manufacturing for 13″ rims is probably an expensive and frustrating business for whoever has the tire supply contract. Not to say that Pirelli have done a reasonable job but now is the time to come up to the Industry spec of 15″ rims and allow competition between tire manufacturer’s while keeping the the rules for different compounds to be used in a race. Small change, more relevance and better racing…..maybe.

15″ sounds like a good compromise, perhaps the relevant aero could still work with some tweaking, same for the suspension. But, McLaren’s pull-rod front suspension threw out the aero for the rear of the car, so I don’t hold that much hope for that..

The only reason road going sports cars started growing bigger wheels in the ’90s was to house bigger brakes. There is absolutely no reason to increase wheel size unless the FIA is going to allow bigger disks and calipers.
Increasing unsprung weight is never a good idea.

The low profile tyre was created for Porsche in the early/mid 1970s. Once Porsche put a turbo on the 911 engine, power created a new problem: how to stop the car. Porsche had a brake design — borrowed from the 917 — but it didn’t fit inside the wheel.

The regulations for GT racers (911 RSR or 934) limited how much the wheel arches might be flared etc so Porsche could not fit a bigger conventional rim and tyre. Porsche convinced a tyre manufacturer (Pirelli, I believe) to create low profile tyres for them — a bigger rim diameter but similar external diameter with the tyre fitted. Immediately, Porsche could fit 917 style brake disks and calipers, and the GT racers stopped better.

The first low profile tyres weren’t all that skinny. There was a 10% difference in aspect ratio, accommodated in the basic suspension design.

Then sports car racing rules changed. Group 5 regs allowed more extensive body modifications. Low profile tyres were no longer required in the categories where Porsche raced as a factory team, but customers needed them in Groups 3 and 4. Porsche thus continued to homologate low profile wheels and tyres for the 911 family.

And every other manufacturer thereafter sought low profile tyres.

Note that some Porsche road cars were designed to suit racers, although a few 911 RS drivers may have saved their necks owing to great brakes. When discussing relevance of racing technology, we have to ask questions. Is whatever tech “relevant”? Do you use it or has it been imposed upon you by a marketing department?

Super Seven asks valid questions about brake size and unsprung weight. My understanding is that designers reduced brake size (2014) in response to the rules permitting energy recovery and that they are free to change those designs. As for unsprung weight, yes it is undesirable, but any increase inside current rims would be to last year’s weight; it is a change that could be quickly understood.

The way I see it is road cars should move back toward the lighter-smaller philosophy of F1 – NOT the other way around!

The current F1 small rim-high profile tyre combination will always be more efficient in terms of accelleration and fuel economy due to the mass being more central/axial and less circumferential/peripheral. That said, if speeds were constant (hardly in F1) then you would gain some efficiency in the flywheel effect of more mass toward the circumference.

Historically, car wheels got bigger as cars became larger and heavier! More was power needed to deal with the car’s increased mass and increased frontal area so consequently the brake disc size had to increase for reasons of safety – hence the need for a bigger diameter rim. Eventually, designers learned how to scale wheels to ‘aesthetically suit’ a BIG bloated car. Same is true of the increase waist height and proportional reduction in window size …all to appeal to the eye, having shot themselves in the foot with increasing car size and weight! With car weight increase more GRIP is achieved by increasing the overall tyre diameter because larger diameters have a larger longitudinal contact patch – and the std width also increased on normal cars for the same reason (heavy cars) and to control the increased mass in a corner with a larger transverse contact patch.

So to my mind – large diameter wheels are synonymous with BIG heavy cars whether the tyres are high profile (heavy trucks) or extremely low profile (heavy supercars).

Yes – you get sharper turn-in with low profile tyres but the rate limiting factor will always be GRIP – a light rear engined car in the wet on low profile tyres has little inherent front-end grip compared to a front-engined heavy car so will still understeer off the track dependent on factors of speed/downforce, and the heavier car (with little downforce) will always GRIP better in the wet.

So lets keep F1 wheels and tyres as they are and b*ll*cks to popular-culture aesthetics unless, like Barry boys, your brain only engages when you see elastic bands on pram wheels …

I thought the tyres would actually be lighter as there is less rubber. The wheels are made from very light alloys so their weight increase would not be as bad. This is assuming that we are talking about an actual increase in the wheel rim and not the tyre diameter yes? That’s what 18″ wheels refer to, not an increase in the tyre diameter?

If the quality of the roads in the UK are anything to go by then we’ll be heading towards more tyre wall and smaller wheels soon to protect against pinch flats and wheel damage from pot holes… Perhaps F1 should predict this and meet somewhere in the middle of 13-18″? 😉

Agreed. My golf has 17″ rims for the summer and 16″ winter rubber for the winter (surprisingly..) There is quite a difference between the two, made even worse by the appalling state of the roads in the UK.

I think this would be a positive change for F1, beyond simple aesthetics. Far more road relevant to today’s tires, more for the teams to develop regarding suspension, ride height, braking, etc, which also are all more road relevant. Sounds like the new tyres would fundamentally (rather than artificially) take away from aero, which I think would be another positive (and more road relevant) change.

If Pic is right and it really cuts the aero that much isn’t that the magic bullet and the FIA should implement this asap? (assuming they can’t crawl most of it back immediately) Sure beats the ugly narrow track cars or ridiculously proportioned wings we have now.

Joe – Add to everything negative you’ve said here ; The fact that switching to 18″ wheels will once again cost the teams already strapped for cash a bloody fortune in suspension design and development [ since with the 13 inchers the tires act as a major part of the suspension .. providing damping as well as grip ] .. the reality that low profile wheels and tires handling tapers off dramatically below a certain weight [ F1 cars weigh well below that critical threshold ] … and on and on .. et al .. ad infinitum . Once again a very expensive and complicated solution to a problem that does not exist … this time brought to you by the fine folks at Pirelli and the FIA . I mean seriously . Can we finally come to grips with the fact that nothing on a modern era race car … especially at the level of F1 [ or LeMans prototypes for that matter ] is relevant what so ever to road cars … be done with it .. and get on with the design of race cars , tires etc .. for race tracks only … that might actually prove enjoyable to watch and see evolve … and leave all the road car relevance pretense behind ?

So Joe ….. I’ll reiterate the most excellent question you asked a bit ago . Why is the FIA and the powers that be so damned and determined to bring down F1 with each and every move such as this ?

Joe, as we have seen problems with braking on the existing small discs then presumably with a larger rim this will presumably allow a larger brake disc – I’M NO BRAKE ENGINEER but presumably with a larger rim this will allow (as per road cars) increased braking ability, control and longevity ????

In this case I think you are blaming the wrong people my read on this is pretty simple. It’s Pirelli trying to do a sell job on Formula 1 and FIA to get something more marketable for their own purposes simple as that.

Michelin already has excellent 18″ technology from Sportscars and tyres which are grippy, durable, marbleless and can last an hour taking up to 1000bhp through them and therefore…. …… but all that is meaningless ……. they are French !!! (Nuff said !! )

I still get the impression that the Michelin tyres the teams used, were still way more advanced than the tyres they use today. I understand Michelin have created a slick tyre that can be used as a wet weather tyre, compared to the Pirellis wets with groves that barely work and require a safety car every time there is a shower.

I mean, I think I know how, but I can’t still get it around my head that there’s no choice.

Maybe just maybe a lot is going to break up, rules wise, and what will happen is this:

~ no supplier gets a inbuilt advantage
~ that scares the others away, if not legislated against
~ that causes each supplier to hedge their bets
~ that means there are more conservative bets on the tech
~ that results in more companies each spending less
~ that doesn’t do a very bad thing to all the motorsport companies at all

I’d better check that spare room is both darkened enough, and the cool breeze is flowing, now…

Maybe my question is a different way: is it right in the way of competition to allow any tyre supplier to come in as they want? Oh, compound question, TV unilateral avoiding any real question style, for the benefit of viewers in Strasbourg… does testing limits prevent competition, and does by that lack of competition, any grace of assumption this is the pinnacle of motorsport, thereby become moot?

I think we’ve always accepted a certain amount of artificiality when the racing is good. But I think this year has been great because of flexibility through the rules, because of the PU newness, and there is no evidence to say less money is spent by regulation.

It’s a odd thing, to claim exemption from normal rules by being exalted, but not being exalted by reach of any other standards of attainment. Maybe the self defining nature of F1 really is all that it is about….

Speaking purely personally as a long term F1 enthusiast interested primarily in racing, I would like to see an increase in the importance of mechanical grip over aerodynamics. I like the idea of drivers wrestling with cars and gladiatorial battles like Vettel’s and Alonso’s and Silverstone (with the benefit of modern safety). If there is a secondary benefit to road cars, so much the better.

F1 today, however, seems to be positioned somewhere between the automotive and aerospace industries, so I’m guessing ‘relevance’ is an imprecise term. As I have no interest in aircraft, my sympathies are with four wheels but the reality is probably different.

Whatever, the Silverstone test was with a car totally unsuited to the prototype tyres, making many conclusions premature. As car design evolves incredibly rapidly, even without imposed changes, I have absolutely no doubt whatsoever that F1’s finest will come up with fast, driveable and exciting cars no matter what the size of the wheels. Every era has had its highlights and its greats; the next one will be no different.

The designers will always improve any part of the car which provides the greatest benefit – and therefore I would expect after a year to see virtually no change in speeds or fuel efficiency but we should question whether we would see improved Racing. I’m no driver or designer but the way I see it is :-

– Larger rim – better structural integrity to the rim/ tyre combination therefore a driver has more control over his vehicle. There is far less of a lateral sponginess (for want of better expression) between the rim direction and where he wishes to position his vehicle = A rise of those drivers who have that instant feel / touch / positioning / be it in corners or when dicing with another car or positioning to overtake. = A definite improvement.

Some good comments here as usual but i think most miss the point. Change will come because there is a hybrid engine in the back of an F1 car, This change came about to keep the engine suppliers happy and to make the technology more relevant to their business of designing and selling cars and making money. (I’m personally very impressed with it as well.) Now we come to look at tires (sorry my lap top speaks American, not me) and a single manufacturer producing batch after batch of specialist rubber for 13″ rims. We have already started down this road of providing relevance to F1 with engines, surely the next step is a small change up a size to 15″ industry standard, I’m thinking a lot of cost savings on brakes suspension, rims, tires etc. The 18″ rim is a red herring thrown out there to deflect from the obvious solution.

I’ve worked in and around the show along time ago, and understand a little of the thought process of the engineers and the necessity to be a little devious to obtain the goal which you really want. 18″ rims and wheels have been thrown out there to cover the fact that the major teams have been instructed to find a cost saving to hold up and show that they are trying to reduce costs to appease the poorer end of the grid. Relevance to the real world matters not to a team but the FIA still make the rules. After a lot of meetings and talk the 15″ compromise will be proposed and accepted. Small change, cheaper parts, possibility of a good old fashioned tire war and more money in the budget for other ideas.Just my thoughts but time will tell. Have a great day Y’all!

Joe
Moving away from all the tech above, once I read that F1 tyres and rims were 13″ to allow for a higher sidewall and though have the supplier putting his name in BIG LETTERS on them, so everyone could read it, alive or in TV….pure marketing…. Does that make any sense, have you read or heard about it? Thanks

Joe,
Can you clarity your comment on the increase in weight and increased fuel consumption of large (18-inch) rims verus small (13-inch) rims? Was that based upon an F1 wheel/tyre design or taken from road car tyres. If it is from road car wheels the increased weight is easily explained (and as such would not be seen on F1 cars) For example a BMW 3-series can run on 16-inch rims (with 205/55 R16 tyres) or it can have 18-inch wheels with 255/35 R18 tyres.. You’ll notice that the larger wheel is also much wider and hence heavier due to the increased amount of rubber across the width of the tyres.

In the case of going from 13 to 18 in F1, we must assume that the tyre width and outside diameter are the same and hence there is no increase in width. As someone has already pointed out, the increase in metal for the larger rim is more than made up by less sidewall (and rubber) in the tyre and so the weight should not increase (at worst. I’d say it would stay the same). By similar argument, the increased fuel consumption would also not happen as the aerodynamic drag would be the same as we are not going from narrow tyre to wide tyre as is the case in road cars.

Some time ago I read an article about F1 going to larger wheel sizes. the overall conclusion was that there would be an increase in performance. Factors include lower unsprung weigh and more consistent contact patch. In addition the more rigid wheel/tyre combination would improve turn-in, as has been commented on in previous posts

It would have been a little more revealing had Pirelli brought some 20 and 22 inch rims and maybe 24 inch as well. These are all available in road car mode if one goes looking for spare wheels and tyres.

One of the anticipated problems of this season was expected to be wheelspin, a difficulty in getting the vastly increased torque down on to the track. One of the most obvious solutions was to use bigger wheels ie those having a bigger effective rolling radius.
Obviously the result of using bigger wheels is that the car goes faster for the same angular velocity of the wheel. With traction control still prohibited this would seem to be a reasonable solution to using the torque, which is currently being wasted.

rpaco – going for larger wheel/tyre diameters as you suggest would be no different to changing the gear ratios (in terms of torque transmission – although there would be a minor change in the contact patch shape).
I would suspect that if/when the 18-inch rims are introduced, the outside diameters and widths of the tyres would be the same as today (or at least very close)
As for the brake regulations, they may indeed need changing as it would be possible to install much larger brake components. Having said that I think the brakes are already grip-limited as it is so easy for them to lock-up when applied, but perhaps a re-design to use a larger available diameter may save weight and hence further reduce the unsprung weight.

rpaco – going for larger wheel/tyre diameters as you suggest would be no different to changing the gear ratios (in terms of torque transmission – although there would be a minor change in the contact patch shape).
I would suspect that if/when the 18-inch rims are introduced, the outside diameters and widths of the tyres would be the same as today (or at least very close)
As for the brake regulations, they may indeed need changing as it would be possible to install much larger brake components. Having said that I think the brakes are already grip-limited as it is so easy for them to lock-up when applied, but perhaps a re-design to use a larger available diameter may save weight and hence further reduce the unsprung weight.

They’re grip limited at lower speeds, but at top speed it is limited by available brake torque due to the high downforce. There is no modulation, just jam the brakes as hard as you can, and then bleed them off as speed and, more importantly, downforce decreases…. That was the case a few years ago anyway, and I don’t think anything had changed too dramatically.

I’m surprised no one has mentioned the effect on brakes. With larger diameter rims you can fit larger diameter discs, thus more powerful brakes, or more efficient brakes (less braking effort for the same braking effect). The larger disc size increases the heat sink properties, thus less cooling required, and so improved aerodynamics.

At the moment the front brake on a formula 1 car is engineered to fit inside a 13″ rim, imaging what they could do inside and 18″ rim!

“The regulations mandating 13-inch rims in F1 are a legacy of a rule introduced to prevent teams fitting larger-diameter wheels to allow bigger brake discs. As brake disc size is now regulated, this is no longer a concern.” — Craig Scarborough, Autosport

I see the brake disc diameter and thickness are regulated but see nothing regarding the brake pads – apart from the number (a max of two per disc). How far around the discs do the pads go? And would a regulation on the pad area make a difference?